Let’s see what’s new in PLoS ONE, PLoS Biology, PLoS Medicine and PLoS Neglected Tropical Diseases today. As always, you should rate the articles, post notes and comments and send trackbacks when you blog about the papers. You can now also easily place articles on various social services (CiteULike, Mendeley, Connotea, Stumbleupon, Facebook and Digg) with just one click. Here are my own picks for the week – you go and look for your own favourites:
Long-Term Functional Side-Effects of Stimulants and Sedatives in Drosophila melanogaster:
Small invertebrate animals, such as nematodes and fruit flies, are increasingly being used to test candidate drugs both for specific therapeutic purposes and for long-term health effects. Some of the protocols used in these experiments feature such experimental design features as lifelong virginity and very low densities. By contrast, the ability of both fruit flies and nematodes to resist stress is frequently correlated with their longevity and other functional measures, suggesting that low-stress assays are not necessarily the only useful protocol for testing the long-term effects of drugs. Here we report an alternative protocol for fruit fly drug-testing that maximizes reproductive opportunities and other types of interaction, with moderately high population densities. We validate this protocol using two types of experimental tests: 1. We show that this protocol detects previously well-established genetic differences between outbred fruit fly populations. 2. We show that this protocol is able to distinguish among the long-term effects of similar types of drugs within two broad categories, stimulants and tranquilizers. Large-scale fly drug testing can be conducted using mixed-sex high-density cage assays. We find that the commonly-used stimulants caffeine and theobromine differ dramatically in their chronic functional effects, theobromine being more benign. Likewise, we find that two generic pharmaceutical tranquilizers, lithium carbonate and valproic acid, differ dramatically in their chronic effects, lithium being more benign. However, these findings do not necessarily apply to human subjects, and we thus do not recommend the use of any one substance over any other.
Two distinct cortical areas in the frontal lobe of the human brain, known as Broca’s region, are involved with language production. This region has also been shown to exist in nonhuman primates. In this study, we explored the precise neural connectivity of Broca’s region in macaque monkeys using the autoradiographic method to achieve a level of detail impossible in the human brain. We identified two major streams of connections feeding into Broca’s area: a ventral stream from the temporal region, which includes areas processing auditory, multisensory, and visual information and a dorsal stream originating from the inferior parietal lobule and the adjacent superior temporal sulcus. Our detailed connectivity analysis illuminates the pathways via which posterior cortical areas can interact functionally with Broca’s region, in addition to contributing to an understanding of the evolution of language. We suggest that a fundamental function of Broca’s region is to retrieve information in a controlled strategic way from posterior cortical regions and to translate this information into action. This fundamental function was adapted during evolution of the left hemisphere of the human brain to serve language.
A stimulus approaching the body requires fast processing and appropriate motor reactions. In monkeys, fronto-parietal networks are involved both in integrating multisensory information within a limited space surrounding the body (i.e. peripersonal space, PPS) and in action planning and execution, suggesting an overlap between sensory representations of space and motor representations of action. In the present study we investigate whether these overlapping representations also exist in the human brain. We recorded from hand muscles motor-evoked potentials (MEPs) induced by single-pulse of transcranial magnetic stimulation (TMS) after presenting an auditory stimulus either near the hand or in far space. MEPs recorded 50 ms after the near-sound onset were enhanced compared to MEPs evoked after far sounds. This near-far modulation faded at longer inter-stimulus intervals, and reversed completely for MEPs recorded 300 ms after the sound onset. At that time point, higher motor excitability was associated with far sounds. Such auditory modulation of hand motor representation was specific to a hand-centred, and not a body-centred reference frame. This pattern of corticospinal modulation highlights the relation between space and time in the PPS representation: an early facilitation for near stimuli may reflect immediate motor preparation, whereas, at later time intervals, motor preparation relates to distant stimuli potentially approaching the body.
Lévy flights are random walks, the step lengths of which come from probability distributions with heavy power-law tails, such that clusters of short steps are connected by rare long steps. Lévy walks maximise search efficiency of mobile foragers. Recently, several studies raised some concerns about the reliability of the statistical analysis used in previous analyses. Further, it is unclear whether Lévy walks represent adaptive strategies or emergent properties determined by the interaction between foragers and resource distribution. Thus two fundamental questions still need to be addressed: the presence of Lévy walks in the wild and whether or not they represent a form of adaptive behaviour. We studied 235 paths of solitary and clustered (i.e. foraging in group) fallow deer (Dama dama), exploiting the same pasture. We used maximum likelihood estimation for discriminating between a power-tailed distribution and the exponential alternative and rank/frequency plots to discriminate between Lévy walks and composite Brownian walks. We showed that solitary deer perform Lévy searches, while clustered animals did not adopt that strategy. Our demonstration of the presence of Lévy walks is, at our knowledge, the first available which adopts up-to-date statistical methodologies in a terrestrial mammal. Comparing solitary and clustered deer, we concluded that the Lévy walks of solitary deer represent an adaptation maximising encounter rates with forage resources and not an epiphenomenon induced by a peculiar food distribution.
The UK Medical Research Council defines complex interventions as those comprising “a number of separate elements which seem essential to the proper functioning of the interventions although the ‘active ingredient’ of the intervention that is effective is difficult to specify.” A typical example is specialist care on a stroke unit, which involves a wide range of health professionals delivering a variety of treatments. Michelle Campbell and colleagues have argued that there are “specific difficulties in defining, developing, documenting, and reproducing complex interventions that are subject to more variation than a drug” . These difficulties are one of the reasons why it is challenging for researchers to systematically review complex interventions and synthesize data from separate studies. This PLoS Medicine Debate considers the challenges facing systematic reviewers and suggests several ways of addressing them.
Schizophrenia is a lifelong, severe psychotic condition. One in 100 people will have at least one episode of schizophrenia during their lifetime. Symptoms include delusions (for example, patients believe that someone is plotting against them) and hallucinations (hearing or seeing things that are not there). In men, schizophrenia usually starts in the late teens or early 20s; women tend to develop schizophrenia a little later. The causes of schizophrenia include genetic predisposition, obstetric complications, illegal drug use (substance abuse), and experiencing traumatic life events. The condition can be treated with a combination of antipsychotic drugs and supportive therapy; hospitalization may be necessary in very serious cases to prevent self harm. Many people with schizophrenia improve sufficiently after treatment to lead satisfying lives although some patients need lifelong support and supervision.
Suicide is a leading cause of death worldwide. Every 40 seconds, someone somewhere commits suicide. Over a year, this adds up to about 1 million self-inflicted deaths. In the USA, for example, where suicide is the 11th leading cause of death, more than 30,000 people commit suicide every year. The figures for nonfatal suicidal behavior (suicidal thoughts or ideation, suicide planning, and suicide attempts) are even more shocking. Globally, suicide attempts, for example, are estimated to be 20 times as frequent as completed suicides. Risk factors for nonfatal suicidal behaviors and for suicide include depression and other mental disorders, alcohol or drug abuse, stressful life events, a family history of suicide, and having a friend or relative commit suicide. Importantly, nonfatal suicidal behaviors are powerful predictors of subsequent suicide deaths so individuals who talk about killing themselves must always be taken seriously and given as much help as possible by friends, relatives, and mental-health professionals.